Thermite, also referred to as thermit, is a metallic composition of an oxide and aluminum powder. The oxide is typically of iron or magnesium, and may be of other metal. Thermite, as its name implies, provides an extremely exothermic reaction. It offers a compact fuel substance inasmuch as solid metal fuel and solid carburent are intimately mixed. However, the thermite reaction is difficult to control, due in part to the high amounts of heat energy released, which further serves to ignite the fuel, and due to the rapid rate at which the metal fuel is consumed by the combustion. It is used in welding and in incendiary bombs.
Numerous methods have been employed for initiating the combustion of thermite. One known method involves burning metal wires or bars by combusting gases around the metal. In U.S. Pat. No. 2,744,742 there is disclosed the use of a nozzle for introducing combustible gases, such as acetylene, to the vicinity of metal fuel wire. It is not disclosed, however, how the heat produced from the resultant combustion of metal is retained or controlled.
Other methods of combusting thermite include the use of gunpowder (See e.g., in U.S. Pat. No. 2,744,742) and the use of an electrical ignition. The use of an electric spark and percussion cap is suggested for the ignition of thermite in U.S. Pat. No. 1,506,323, which discloses an exothermic apparatus that controls the rate of combustion of metal fuel by providing a mixture of a metal fuel and a normally solid carburent in a "mushy condition" to a combustion chamber. Thermite is used merely to bring the system to operative condition, and is not used as the primary fuel. The apparatus disclosed, moreover, is complicated and bulky.
In view of the foregoing disadvantages, what is needed is a compact and efficient furnace for initiating and controlling the combustion of thermite in a solid, dry form.